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Compound-Specific Hydrogen Isotope Ratios of Sedimentary N-Alkanes: A

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Compound-Specific Hydrogen Isotope Ratios of Sedimentary N-Alkanes: A Compound-specific hydrogen isotope ratios of sedimentary n-alkanes: a new palaeoclimate proxy Dissertation Zur Erlangung des akademischen Grades doctor rerum naturalium (Dr. rer. nat.) vorgelegt dem Rat der Chemisch-Geowissenschaftlichen Fakultät der Friedrich-Schiller- Universität Jena von Diplom-Geologe Dirk Sachse Geboren am 24.09.1974 in Halle/Saale Gutachter: 1. PD Dr. Gerd Gleixner (Max-Planck Institut für Biogeochemie Jena) 2. Prof. Reinhard Gaupp (Friedrich-Schiller Universität Jena) 3. Prof. John M. Hayes (Woods Hole Oceanographic Institution, Massachustetts, U.S.A.) Datum der öffentlichen Verteidigung: 29. Juni 2005 Index INDEX.............................................................................................................................................................................3 1. INTRODUCTION.................................................................................................................................................5 1.1. OBJECTIVES......................................................................................................................................................7 1.2. THESIS ORGANISATION ...................................................................................................................................7 2. METHODS/STRATEGIES.................................................................................................................................9 2.1. SAMPLE SITES AND FIELD SAMPLING.............................................................................................................9 18 2.2. ANALYSIS OF WATER SAMPLES FOR δ O AND δD .......................................................................................12 2.3. SAMPLE PREPARATION, BIOMARKER IDENTIFICATION AND QUANTIFICATION............................................12 2.4. GAS CHROMATOGRAPHY TEMPERATURE CONVERSION ISOTOPE RATIO MONITORING MASS SPECTROMETRY (GC-TC-IRMS) FOR ANALYSIS OF δD ON THE N-ALKANES .......................................................13 2.5. CALCULATION OF THE ISOTOPIC FRACTIONATION ε.....................................................................................14 3. HYDROGEN ISOTOPE RATIOS OF LACUSTRINE SEDIMENTARY N-ALKANES RECORD MODERN CLIMATE VARIABILITY...................................................................................................................15 3.1. INTRODUCTION ..............................................................................................................................................15 3.2. RESULTS AND DISCUSSION............................................................................................................................16 3.2.1. n-alkane concentrations ..........................................................................................................................16 3.2.3. δD and δ18O values of water....................................................................................................................17 3.2.4. δD values of the n-alkanes .......................................................................................................................19 3.2.4.1. δD values of the even carbon numbered short-chain n-alkanes (n-C12, n-C14, n-C16, n-C18, n-C20) and n-C13 and n-C15............................................................................................................................................................................ 20 3.2.4.2. δD values of the n-C17, n-C19, n-C21, n-C23 alkanes.............................................................................22 3.2.4.3. δD values of the even carbon numbered medium to long-chain n-alkanes (n-C22, n-C24, n-C26, n- C28, n-C30) ............................................................................................................................................................24 3.2.4.4. δD values of the odd carbon numbered long-chain n-alkanes (n-C25 to n-C31) ................................25 3.3. CONCLUSIONS................................................................................................................................................26 4. COMPOUND-SPECIFIC δD VALUES OF N-ALKANES FROM TERRESTRIAL PLANTS ALONG A CLIMATIC GRADIENT – IMPLICATIONS FOR THE SEDIMENTARY BIOMARKER RECORD ......................................................................................................................................................................30 4.1. INTRODUCTION ..............................................................................................................................................30 4.2. RESULTS AND DISCUSSION............................................................................................................................31 4.2.1. n-alkane concentrations of biomass ....................................................................................................31 4.2.2. δD values of n-alkanes .............................................................................................................................34 4.2.2. Hydrogen isotope fractionation between source water and biomass n-alkanes ..............................37 4.2.3. Comparison with sedimentary n-alkane distributions and δD values...............................................39 4.3. CONCLUSIONS................................................................................................................................................42 5. SEASONAL VARIATIONS IN DECIDUOUS TREE LEAF WAX N-ALKANE δD AND δ 13C VALUES: IMPLICATIONS FOR THEIR USE AS A PALAEOCLIMATE PROXY ...................................44 5.1. INTRODUCTION ..............................................................................................................................................44 5.2. MATERIALS AND METHODS ..........................................................................................................................45 5.2.1. Study site and sample collection ..............................................................................................................45 5.2.2. Meteorological measurements at the Hainich site .................................................................................46 5.2.3. Modelling leaf water isotopic enrichment...............................................................................................46 5.3. RESULTS.........................................................................................................................................................48 5.3.1. n-alkane concentrations ...........................................................................................................................48 5.3.2. n-alkane δD and δ13C values ...................................................................................................................50 5.4. DISCUSSION....................................................................................................................................................52 5.4.1. Seasonal variations in n-alkane concentration.......................................................................................52 5.4.2. Seasonal variations in n-alkane δD and δ13C values for Maple leaves................................................52 5.4.3. Seasonal variations in n-alkane δD and δ13C values for Beech leaves - Comparison of modelled leaf water enrichment with n-alkane δD values .......................................................................................................54 5.4.4. Implications for the use of n-alkane δD values as a palaeoclimate proxy ...........................................60 6. CONCLUDING REMARKS.............................................................................................................................61 7. SUMMARY..........................................................................................................................................................66 8. ZUSAMMENFASSUNG....................................................................................................................................68 ACKNOWLEDGEMENTS.......................................................................................................................................71 9. REFERENCES....................................................................................................................................................73 Introduction 1. Introduction The reconstruction of past climate variability can provide valuable information on the causes, timing and magnitude of climate change. Since direct observational evidence for climatic changes is available only for the past 100 years, so-called palaeoclimate proxies (e.g. isotope ratios, pollen data, palaeontology, sedimentological methods etc.) can provide us with a better understanding of natural climate variability and it’s forcing mechanisms. Analysis of ice-cores from the polar regions and sediments have provided valuable information on the natural climate variability throughout the geological time. The obtained data are used to evaluate climate models, which are needed to predict possible scenarios of anthropogenic climate change. However, even with the improved knowledge of the climate system components obtained over the last years, it is evident that the interactions between the biosphere, atmosphere, lithosphere and especially the hydrosphere are, despite their generally accepted importance, still poorly understood. Research on dynamics
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